Wireless communications are implemented by any of a variety of radio technologies, depending on the type of application. Cellular phones, for example, may use the Global System for Mobile communications (GSM™), the IS-54 Time Division Multiple Access (TDMA) or the IS-95 Code Division Multiple Access (CDMA) radio technologies, whereas a wireless local area network may use Wi-Fi™, Bluetooth™ or ZigBee® radio technologies. In an ad-hoc, or peer-to-peer, network, a wireless device communicates directly with another wireless device. In an infrastructure network, a wireless device communicates with another wireless device through one or more intermediary gate devices, such as a base station or an access point. Generally, a wireless device uses a single radio technology to effect communication with its peer (in the case of a peer-to-peer network) or with the access point (in the case of an infrastructure network). In the prior art, dual radios are used in a wireless device to support different air interface standards, in order to provide compatibility with different wireless service providers. For example, a dual-radio device may support GSM, a cellular phone service, and Wi-Fi, a wireless Local Area Network (LAN) service, and uses one of these two radios for communication, depending on which service (GSM or Wi-Fi) is available in a geographic area. Generally, such a wireless device selects and uses a single radio for the duration of the connection or service.
The present invention relates to an innovative wireless communications system employing multiple radios. The communications system selects amongst and switches between multiple radios—possibly multiple times—while a connection or session is in progress. This switching allows the communications system to achieve one or more of the following performance objectives:                Maximize communications reliability and robustness against interference and other impairments        Minimize interference to co-existing users        Minimize power consumption        Accommodate any disparity between the uplink and downlink bandwidths        
Moreover, the multiple radio system can reduce the physical footprint of the radio nodes and lead to improved data rates and communication range.
When a single radio type is used, the degrees of freedom are limited for desired optimization. A given radio can be optimized, for example, by the following means:                Switch transmission channels within the given band to dynamically mitigate interference (to improve reliability).        Adjust transmitted power as needed (to improve power dissipation or reliability).        
There are few other meaningful operations that can be performed to optimize single-radio systems. With a single type of radio, it is particularly challenging to design a system that calls for simultaneous optimization of multiple factors—for example, optimization of all of these four factors: link range/reliability, node power, node cost and low interference to other radios. If a radio is optimized for one factor, it will typically negatively impact other factors. For example, if power is reduced for a low-power design, it would typically reduce the range/reliability. If an ultra-wideband (UWB) radio is deployed to cause minimum interference to other radios, it would result in short range, high complexity and potentially high cost (the UWB receiver being complex and high power).
Accordingly, a radio scheme is desired for a wireless communication system that addresses the optimization of multiple factors.